Phosphate ester based lubricants and hydraulic fluids have long service life and excellent stability. Such fluids are typically based on triaryl phosphates. It is known that from use over a period of time phosphate ester fluids experience degradation which is manifested as increased acidity. This acidity may eventually build to corrosive levels.
A wide variety of methods ar used to deal with the problem of acid buildup in phosphate ester fluids. Acid acceptors such as epoxides may be added to phosphate ester fluids. However, acid neutralization agent byproducts may accumulate and may lead to other problems.
Another treatment for overly acidic phosphate ester fluids is contact with neutralizing clays such as Fuller's Earth. A disadvantage of Fuller's Earth treatment is that alkaline earth ions are transferred from the clay into the neutralized ester fluid.
Phosphate ester fluids may also be refined by distillation at reduced pressure. Distillation is effective in purifying organophosphates but this technique demands special equipment and careful process controls. It is desirable to develop improved methods of treating phosphate ester fluids which maintain low acidity without difficult methodolgy or expense.